1. Field of the Invention
The present invention is directed to a method and to a device for manufacturing an endless band of plastic for an intermediate carrier band in an electrographic printer or copier.
2. Description of the Related Art
Intermediate carrier bands are utilized in electrographic printers or copiers in order to generate latent electrostatic images and/or to offer a carrier for toner images to be transfer-printed. For example, an endless band with a photoconductive layer, for example an OPC band (Organic PhotoConducting material) is employed as intermediate carrier band, this forming a corresponding electrostatic charge image, what is referred to as a latent charge image, by being exposed according to a predefined image pattern. This latent charge image is then inked with toner material in a developer station; later, this toner image is transferred onto paper or some other recording medium and is fixed thereon.
An endless intermediate carrier band can also serve as transfer band for collecting toner images and conveying these to a transfer printing location. Given, for example, a multi-color printing, a first toner image of a first color is transferred onto the intermediate carrier band. Subsequently, a second toner image with a second color is transferred onto this first toner image, etc. The multi-colored toner images on the intermediate carrier band superimposed on one another in this way are then conveyed to a transfer printing station and transferred onto the recording medium thereat and fixed.
Ends of a plastic film must be connected to one another for manufacturing an endless intermediate carrier band. The weld that thereby arises can be the cause of numerous disruptions. For example, a thickening along the weld leads to increased wear due to circulation of the intermediate carrier band. Moreover, the material properties can have been changed in the region of the weld, so that this region can generally not be used as a photoconductive region or as a region for the acceptance of a toner image.
German Patent Document DE 19 832 168 A1 discloses a method and an apparatus for welding thermoplastic synthetics using laser light. The ends of a thermoplastic plastic film are arranged abutting and can be held with the assistance of a retainer elements and a silica glass plate. Laser light is coupled in via the silica glass plate, as a result whereof the ends of the film are welded to one another. Special measures for producing a uniform weld are not disclosed.
German Patent Document DE 19 516 726 A1 discloses a method for shaping and closing a folding box, whereby plastic layers for packing a welded to one another upon employment of radiation. The welding process is promoted by applying pressure.
German Patent Document DE 3 713 527 A1 discloses the welding of plastic parts whose ends are place flush against one another. The plastic parts are provided with profiles at their ends, so that these profiles can engage in one another. The ends with the profiles are then welded to one another with the assistance of a laser welding device.
European Patent Document EP-A-0 705 682 discloses a method for the thermal joining of substrates of polymers, whereby at least one substrate is coated with a medium that absorbs microwaves. The substrates are then welded to one another in a microwave field.
Internet information of the EWi WELDNET company with the title “Hot Plate Welding”, obtainable under http://www.ewi.org/matjoin/plastics/ttir.html; http://www.ewi.org/matjoin/plastics/hotplate.html; http://www.ewi.org/matjoin/plastics/infrared.html, teaches that plastic parts be firmly joined to one another by means of a butt joint welding. A heating element is thereby placed between the contact surface of the parts to be welded, the surfaces lying opposite one another at their end faces, and the contact surface are heated up to the melting phase. Subsequently, the heating element is removed and the contact surfaces residing opposite one another are pressed against one another. A durable connection between the contact surfaces is provided after cooling. Such a method, however, has the disadvantage that a raised weld projecting out of the surfaces of the parts welded to one another arises at the contact surfaces.
An overlap welding method is disclosed under the titles “Through-transmission Infrared Welding TTIR” or, respectively, “Infrared Heating” in the aforementioned Internet information. The ends of plastic parts to be welded are thereby placed on top of one another and heated up to the melting phase by infrared radiation or laser emission from a radiation source that is not in contact with the parts to be welded. One application of this method is the welding of a part that is transparent for the radiation to a part that is impermeable to the radiation, whereby the welding arises in the region of the surfaces of the parts to be welded that lie on top of one another. A further application of this method is the welding of plastic films lying on top of one another at ends with the assistance of a thin intermediate layer. The method is not suitable for the manufacture of endless bands.